1. Field of the Invention
This invention relates to storage stable, concentrated monosulfonated disazo dye solutions which retain good solubility in hard water.
2. Description of the Prior Art
The use of direct, acid and basic dyes as concentrated aqueous solutions, often referred to in the art as liquid dyes, has become commercially important in the last few years for continuous dyeing of paper and textile goods. The chief advantages of such liquid dyes over dye powders are the avoidance of dusting problems in handling and the great ease and speed of metering the liquid dyes.
The sodium salts of monosulfonated disazo dyes generally have limited solubility in cold water; their solubility is seldom more than 1 weight percent. With the advent of solution dyes for continuous dyeing processes, various methods have been disclosed for preparing 10% to 20% solutions of these dyes for use in said processes. In many cases, lithium salts of the dyes have been found to be more soluble than the more conventional sodium salts. Also alkanolammonium salts have been found to offer improved solubility and other desirable properties, as disclosed in U.S. Pat. No. 2,314,356 and U.S. Pat. No. 3,681,320. In most cases, the aqueous solutions employ a supplementary solvent which is a water-miscible solvent of fairly low molecular weight. Ethylene glycol, glycerin, Cellosolve, Carbitol, and other solvents of this type have been used.
In a copending application of Steven Dombchik, Ser. No. 284,478, filed Aug. 29, 1972, is disclosed a storage-stable, concentrated, aqueous disazo acid dye solution consisting essentially of, on a weight basis,
A. 10-25% OF THE LITHIUM OR TRI(2-HYDROXYETHYL) AMMONIUM SALT OF THE DYE HAVING THE FORMULA ##SPC2##
Wherein one of X and Y is hydrogen and the other is CH.sub.3 and R.sup.1 is --CH.sub.2 CH.sub.2 OH, --CH.sub.2 CH(CH.sub.3)OH or CH.sub.2 CH(C.sub.2 H.sub.5)OH;
b. 5-25% of N-methyl-2-pyrrolidone; and
C. THE BALANCE, TO 100%, WATER.
Although these dye solutions are storage-stable, they, tend to precipitate calcium and/or magnesium salt forms of the dyes when water containing these ions is added to the dye solution.
It is known to immobilize multivalent ions such as Ca.sup.+.sup.+, Mg.sup.+.sup.+ and Fe.sup.+.sup.+.sup.+ by complexing them with the sodium salt of ethylenediametetraacetic acid. For example, U.S. Pat. No. 3,055,726 discloses the use of the sodium salt of ethylenediaminetetraacetic acid and a polymeric alkali metal phosphate in a dye bath containing hard water and sodium carbonate. Summersgill, Journal of the Society of Dyers and Colourists, vol. 70, p. 278-283 (1953), discloses that some recalcitrant wool dyes such as Polar Red RD (CI 23635), a disulfonated azo dye, can be prevented from precipitating in hard water by adding the sodium salt of ethylenediaminetetraacetic acid (see page 279, column 1, lines 17-23).